The invention relates to an arrangement for generating quasi-random sequences in AMI code by use of a generator for binary quasi-random sequences.
The surveillance of transmission circuits for digital signals frequently involved monitoring transmitted digital signals at individual locations of the transmission circuits for infractions of the coding rule employed in the formation of the digital signals. These coding rule infractions arise due to transmission errors. It is a pre-condition for an identification of coding rule infractions that a redundant code exists which allows infractions of the coding rule to be perceived. A code frequently employed in the transmission of digital signals is the so-called AMI code which is a pseudoternary code in which successive one characters are transmitted by means of pulses having alternating polarity, whereas zero characters are allocated to the zero level.
A problem in the surveillance of transmission circuits for digital signals through investigation of such signals for coding rule infractions or violations is the occasional check of the coding rule infraction test units contained at specific locations in the transmission circuit. For this check, for example, AMI-coded test signals are required which are locally generated in response to an additionally transmitted signal. The AMI-coded test signals are also required in a final check after a manufacture of regenerators having code infraction test units.
The generation of AMI-coded signals usually occurs by connecting a spur line in parallel to the output of a generator for test signals present in the differential binary code. Such a spur line is short-circuited at the end and its single signal transit time corresponds to half the bit duration of the signals to be reshaped. A negative pulse, which appears at the input of the spur line one bit duration after the positive pulse, is generated by means of reflection of a positive pulse, for example, at the short-circuited end of the spur line. Such a technique for generating AMI-coded signals, however, is not suitable for generating test signals since the observation of the AMI coding rule is induced by the employment of a spur line whereas the test signals must contain a specific plurality of coding rule infractions.